This invention relates to the field of borehole measurements. More particularly, this invention relates to a method of monitoring the core sampling process of a downhole core acquisition tool so as to detect the presence of an adequate core sample prior to retrieving the core barrel to the surface.
In various downhole drilling operations, it is often necessary to obtain core samples of the strata being drilled. Such core samples are acquired by use of known coring tools which are attached at the end of the drillstring and act to retrieve a cylindrical core sample. However, when drilling a sample core, it is often difficult to determine when the core barrel of the coring tool is full of core and whether or not the core is properly retained in the coring tool. If the drilling personnel on the surface makes an incorrect judgement regarding the status of the core, and thereafter remove (i.e., trip) the drillstring from the hole without receiving sufficient core, then the coring operation must be repeated leading to a substantial waste of rig time and therefore higher drilling costs. It will be appreciated that premature removal of the coring tool prior to acquiring a full core is a fairly frequent and highly undesirable occurrence at a typical drilling site.